
Have eyes in the back of your head
Vigilance Required
Use this phrase when someone needs to be extremely careful or aware of their surroundings. 
Metaphorical Sense
Remember, it's a figure of speech. No one actually has extra eyes; it means being alert and perceptive. 
Not Literally Possible
Don't confuse learners; emphasize the expression is used humorously or jokingly, not to describe a physical ability. 